The objectives if the proposed research are to describe and understand the nature and course of visual impairments caused by retinitis pigmentosa (RP) and to determine and characterize the limitation that RP visual impairments imposed on visual performance. Meeting these objectives is important to understanding the visual consequences of RP over its natural course and to developing optimal visual rehabilitation methods and technology to aid RP . Our past research has establish the existence of two functional subtypes RP. We also have demonstrated that the progressive visual field loss in all forms of RP follows an exponential decay. This decay starts at a "critical age" that differs among patients and differs statistically among functional and genetic subtypes; the time constant of the decay is statistically distinguishable among the RP subpopulations. Using psychophysical methods, we have found evidence for abnormal visual system adaptation, reduce spatial inhibition, abnormal motion processing, increased intrinsic visual noise, and reduced sampling efficiency in the central retina of RP patients. In order to describe and understand the nature and course of RP visual impairments, we propose to conduct several psychophysical studies of the visual processing of space and motion in RP, the proposed studies include measures of spatial contrast sensitivity functions (CSF) using localized stimuli with different time parameters, measures of spatial inhibitory processing (Westheimer functions and contrast thresholds in relation to a luminance step). measures of monocular and binocular hyperacuity thresholds and bias, measures of monocular and binocular motion direction and velocity discrimination thresholds, measures of the role of abnormal neutral adaptation in the elevation of spatial and motion discrimination thresholds, and measures of the role of abnormal intrinsic noise in discrimination thresholds elevation. In order to determine and characterize visual performance limitation in RP, we proposed several studies (many in collaboration with order Wilmer investigators) of reading, face discrimination, visual search, motion perception, and mobility. The results of these studies will lead to an improved understanding of visual impairments that accompany RP progression and the limits that they impose on visual performance during the course of the disease.